The present invention relates to an arrangement for the tensioning and adjusting of a wind-around drive, e.g. a chain drive, by means of which a camshaft of an internal combustion (IC) engine drives a second camshaft, with a relative rotational position of the camshafts being changed by adjustment of the chain drives.
A tensioning and adjusting arrangement for a drive is shown in German Patent Document DE-OS 34 21 028. A tensioning arrangement is applied to a chain drive which winds around the two camshafts of an internal-combustion engine. This tensioning arrangement comprises a hydraulic piston bracing the load end and the loose end of the chain. As an alternative, two separate tensioning devices may also act upon the loose end and the load end of the chain. In addition to the bracing, both arrangements also change the relative rotation of the two camshafts with respect to one another by a lengthening of the load end and a corresponding shortening of the loose end, or vice versa. In this manner, the control times of the inlet valves may be variable, and an optimal performance and low exhaust gas emission can be achieved over the whole rotational speed range of the internal-combustion engine.
It is an object of the present invention to further improve a tensioning and adjusting arrangement of the aforementioned such that a high operational reliability is ensured at low cost.
The foregoing object has been achieved by providing a tensioning arrangement which acts transversely with respect to the chain and which, for adjusting the chain, is shifted transversely to it in such a manner that the loose end of the chain is lengthened and the load end is shortened, or the loose end is shortened and the load end is lengthened.
If a separation of functions takes place such that a tensioning arrangement for the chain is provided which, for adjusting the chain, is shifted transversely to it, the chain is always maintained under tension irrespective of possible disturbances in the adjusting mechanism or its control. This feature ensures a lasting, although not optimal operation of the internal-combustion engine.
In another advantageous further embodiment of the invention, the tensioning and adjusting arrangement comprises an exterior hollow piston, an interior hollow piston which is longitudinally guided in the exterior hollow piston, and a coil spring which is centrally braced between the two pistons as well as a hydraulic connection on the central hollow space. The exterior piston has a second hydraulic connection on its exterior side. When pressure acts on this hydraulic connection, the tensioning device can be shifted transversely with respect to the chain.